JP2001318085A - Padding pipe inspecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a padding pipe inspecting method capable of providing a clear reflection echo when a padding pipe made by padding a metallic pipe having coarse grain structure with a different kind of metal is inspected by an ultrasonic inspection method and capable of surely detecting whether a defect exists in the joint boundary face of the padding pipe or how thick the cladding weld is. SOLUTION: When the size of a reflection echo is detected by launching an ultrasound into the padding pipe 10 made by padding an outer surface or inner surface of the metallic pipe 12 having coarse grain structure with a different kind of metal 14, a longitudinal ultrasonic wave is used having a wide band characteristic, especially a wide band characteristic of frequencies from 3 to 4 MHz. When it is detected whether a defect exists in the joint surface of the padding pipe 10, the position of a gate for echo detection is changed according to the pipe thickness of the metallic pipe 12. The thickness of the cladding weld is found from the difference between the pipe thickness of the metallic pipe 12 measured before padding and the pipe thickness of the padding pipe 10 measured after padding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a cladding tube, and more particularly, to a cladding tube in which a dissimilar metal is clad on an outer surface or an inner surface of a metal tube such as a steel pipe for a plant, a line pipe, and an oil well tube. The present invention relates to a method for inspecting a cladding tube suitable for inspecting for the presence or absence of a defect generated at a bonding interface of the metal and measuring the thickness of the cladding.

[0002]

2. Description of the Related Art Metal tubes used under severe conditions include:
It is required to satisfy a plurality of properties such as strength, corrosion resistance, and thermal fatigue resistance. Since it is difficult to achieve such a plurality of characteristics simultaneously with a metal tube made of a single material, in such a case, a cladding tube in which a different metal is clad on the outer surface or inner surface of the metal tube is used. Used. For example, a cladding tube in which a dissimilar metal with a thickness of several mm is clad for the purpose of improving corrosion resistance on the inner surface of a centrifugally cast tube having a strong crystal structure, since it has both corrosion resistance and heat fatigue resistance, is thermally decomposed. Application to chemical plants such as furnaces is expected.

[0003] The cladding tube is manufactured by a cladding welding method, but in order to satisfy the high required characteristics, there is no defect in the joining interface between the metal tube and the dissimilar metal and the cladding thickness is a predetermined thickness. More than that is required. Therefore, in order to guarantee the quality of the cladding tube, it is necessary to non-destructively inspect the presence or absence of a defect at the bonding interface and the cladding thickness. For such an inspection, generally, an ultrasonic flaw detection method using ultrasonic waves having a frequency of about 1 to 15 MHz is used.

[0004] Further, when inspecting the entire surface of the cladding tube for the presence or absence of a defect, it is not practical to constantly monitor the magnitude of the reflected echo because it requires a huge memory. Therefore, usually, a monitoring area (hereinafter, referred to as a “gate”) at a predetermined time interval is set after a predetermined time has elapsed from the irradiation of the ultrasonic wave, and the maximum output in the gate is set to a certain threshold value. A method of determining the presence or absence of a defect depending on whether or not the number of defects has been exceeded is adopted. As the gate setting method, a surface echo synchronization method and a delay gate method are known. The surface echo synchronization method is a method in which a gate is set after a certain period of time has elapsed since the surface echo was observed. On the other hand, the delay gate method is a method in which a gate is set after a certain period of time has elapsed after transmitting an ultrasonic wave.

[0005]

However, if the frequency of the ultrasonic wave is increased when the crystal grain size of the metal tube is large, such as a centrifugally cast tube, the scattering of the ultrasonic wave at the grain boundary increases, and There is a problem that echo cannot be obtained. On the other hand, when the frequency of the ultrasonic wave is reduced, there is a problem that the resolution is reduced and the measurement accuracy is reduced.

When the surface echo synchronization method is adopted as the gate setting method, it is assumed that the thickness of the metal tube is constant. Therefore, when the thickness of the metal tube is not constant, there is a problem that the gate is displaced from the bonding interface and a defect echo cannot be obtained. On the other hand, the delay gate method is based on the premise that the distance between the metal tube and the ultrasonic probe is constant. Therefore, even if the thickness of the metal tube is constant, if the distance between the metal tube and the ultrasonic probe fluctuates due to force majeure, the gate will be displaced from the bonding interface, and the defect echo will not be obtained. is there.

Further, since the difference in acoustic impedance between the metal tube and the cladding metal is generally small, even if ultrasonic waves are incident on the cladding tube, the reflected echo from the joint interface where the joint is in a good condition is not significant. I can't get it. Therefore, it is difficult to directly determine the build-up thickness by using the ultrasonic flaw detection method.

The problem to be solved by the present invention is to provide a metal tube having a coarse grain structure in which a different type of metal is built up by using an ultrasonic flaw detection method. An object of the present invention is to provide a method for inspecting a filling tube.

Another problem to be solved by the present invention is that the thickness of the metal tube is not constant, or the distance between the cladding tube and the ultrasonic probe is not constant. Even in such a case, an object of the present invention is to provide a method for inspecting a cladding tube, which can reliably detect the presence or absence of a defect at a bonding interface.

Another problem to be solved by the present invention is that even if the difference in acoustic impedance between the metal pipe and the overlay metal is small, the overlay thickness can be measured accurately. An object of the present invention is to provide a method for inspecting a filling tube.

[0011]

In order to solve the above-mentioned problems, the present invention is directed to a method of applying ultrasonic waves to a cladding tube in which a dissimilar metal is clad on the outer surface or inner surface of a metal tube, and the size of a reflected echo is increased. In the method for inspecting a cladding tube having a reflection echo detecting step of detecting the depth, the metal tube has a coarse crystal grain structure, and as the ultrasonic wave, a longitudinal wave ultrasonic wave having a wide band characteristic is used. It is an abstract. In this case, the frequency of the ultrasonic wave is desirably 3 to 4 MHz.

A second aspect of the present invention is a reflected echo detecting step of detecting the magnitude of a reflected echo by irradiating an ultrasonic wave to a cladding tube in which a dissimilar metal is clad on the outer or inner surface of the metal tube. In the method for inspecting a cladding tube provided, the reflection echo detection step is to detect a defect echo caused by a defect generated at an interface between the metal tube and the dissimilar metal,
The gist is that the method further includes a gate position adjusting step of changing a gate position for detecting the defect echo in accordance with the thickness of the metal tube measured before building up.

A third aspect of the present invention is a reflected echo detecting step of detecting the magnitude of a reflected echo by irradiating an ultrasonic wave to a cladding tube in which a dissimilar metal is clad on the outer or inner surface of the metal tube. In the inspection method of the cladding tube provided, the reflected echo detection step is to detect a surface echo caused by the surface reflection of the cladding tube and a bottom echo caused by the bottom reflection, and is measured before the cladding. Said metal tube thickness,
The method further comprises a cladding thickness calculating step of calculating a cladding thickness of the cladding tube from a difference from a tube thickness of the cladding tube obtained from a difference between arrival times of the surface echo and the bottom surface echo. It is the gist.

When inspecting a cladding tube in which a different metal is clad on the outer surface or the inner surface of a metal tube having a coarse crystal grain structure by an ultrasonic flaw detection method, a longitudinal wave ultrasonic wave having a wide band characteristic, particularly, a frequency of 3 to The use of longitudinal ultrasonic waves having a wide band characteristic of 4 MHz makes it possible to suppress the scattering of ultrasonic waves at grain boundaries while maintaining high resolution. Therefore, a clear reflected echo is obtained, and the presence or absence of a defect and the thickness of the overlay can be inspected with high accuracy.

When the gate position is changed in accordance with the previously measured thickness of the metal tube, if the thickness of the metal tube is not constant, or if the thickness of the cladding tube and the ultrasonic probe are different. Even when the distance between them fluctuates, it is possible to reliably detect a defect echo caused by a defect generated on the bonding surface.

Further, after the cladding, an ultrasonic wave is applied to the cladding tube, the thickness of the cladding tube is measured from the difference between the arrival times of the surface echo and the bottom surface echo, and the thickness of the metal tube before the cladding is measured. And the difference between the thickness of the cladding tube and the thickness of the cladding tube, the cladding thickness can be easily and accurately determined even when the difference in acoustic impedance between the metal tube and the dissimilar metal is small.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for inspecting a cladding tube according to the present invention will be described in detail. The method for inspecting a cladding tube according to the first embodiment of the present invention is characterized in that ultrasonic waves are incident on a cladding tube in which a dissimilar metal is clad on an outer surface or an inner surface of a metal tube having a coarse crystal grain structure, and a reflection echo is formed. Is characterized by using longitudinal ultrasonic waves having a wide band characteristic when detecting the magnitude of.

In this case, the frequency of the ultrasonic wave used is 3
-4 MHz is particularly preferred. It is not preferable that the frequency of the ultrasonic wave is on the low frequency side, particularly, less than 3 MHz, because the resolution of the reflected echo decreases. On the other hand, if the frequency is higher than the high-frequency side, in particular, 4 MHz, the ultrasonic waves tend to be greatly attenuated by scattering at the grain boundaries, and a clear reflected echo cannot be obtained. Further, even if the frequency is appropriate, it is not preferable to use an ultrasonic wave having a narrow band characteristic, because the resolution in the thickness direction of the cladding tube is reduced.

The metal pipe on which the dissimilar metal is deposited is preferably one having a crystal grain size of 100 to 1000 μm (for example, a centrifugally cast pipe). When the present invention is applied to a cladding tube provided with a metal tube having such a coarse crystal grain structure, there is an advantage that the detection accuracy of the reflected echo is improved as compared with the conventional method.

FIG. 1 shows the relationship between the frequency characteristics of the ultrasonic waves and the reflection echo when the ultrasonic waves are incident on a metal tube having a coarse crystal grain structure. In FIG. 1, “surface echo” refers to a reflected echo reflected from the incident surface of the ultrasonic wave, and “bottom echo” refers to a reflected light reflected from the surface opposite to the incident surface of the ultrasonic wave. Echo. Further, the “defect echo” refers to a reflected echo reflected from a defect generated on the bonding surface.

As shown in FIG. 1A, in the case where the metal tube has a coarse crystal structure, if a longitudinal ultrasonic wave having a narrow band characteristic of less than 3 MHz is used, a bottom echo can be obtained. The pulse width of the bottom echo becomes wider,
Resolution decreases. Therefore, when the dissimilar metal is clad in such a metal tube, when the cladding thickness is small, it is difficult to clearly separate the defect echo from the bottom echo.

On the other hand, as shown in FIG. 1B, when a longitudinal ultrasonic wave having a narrow band characteristic exceeding 4 MHz is used, attenuation of the ultrasonic wave becomes large and a bottom echo cannot be clearly obtained. For this reason, it is particularly difficult to detect a defect echo caused by a small defect generated at the joint interface between the metal tube and the dissimilar metal.

On the other hand, as shown in FIG. 1C, when a longitudinal ultrasonic wave having a wide band characteristic of a frequency of 3 to 4 MHz is used, a bottom echo with high resolution can be obtained. In addition, since the attenuation of the ultrasonic wave is suppressed, the bottom echo caused by the multiple reflection can be detected. Therefore, even when the metal tube has a coarse crystal grain structure or when the build-up thickness is small, the defect echo and the bottom surface echo can be clearly separated. Further, since high sensitivity is obtained, the presence or absence of a defect can be detected with high accuracy even when the size of the defect is small.

Next, an inspection method according to a second embodiment of the present invention will be described. The inspection method according to the present embodiment is directed to a defect echo caused by a defect generated at a joining interface between a metal tube and a dissimilar metal by irradiating an ultrasonic wave to a cladding tube in which a dissimilar metal is clad on an outer surface or an inner surface of the metal tube. Is detected, the gate position for detecting a defect echo is changed according to the thickness of the metal tube measured before the cladding.

First, the thickness of the metal pipe before the cladding is measured in the circumferential direction and the longitudinal direction of the metal pipe. The method of measuring the thickness of the tube is not particularly limited, but ultrasonic waves are incident perpendicularly to the metal tube, the difference in arrival time of the surface echo and the bottom surface echo of the metal tube is measured, and the tube is measured from the difference. Find the thickness. In this case, the ultrasonic waves may be incident from the outer surface side of the metal tube, or may be incident from the inner surface side.

In the case where the metal tube has a coarse crystal grain structure and the thickness of the metal tube is measured by using ultrasonic waves, as described above, the longitudinal wave ultrasonic wave having a wide band characteristic, It is preferable to use longitudinal ultrasonic waves having a wide band characteristic of a frequency of 3 to 4 MHz. It is desirable to measure the thickness of the metal tube over the entire surface. However, when the variation in the thickness in the longitudinal direction is small, the change in the thickness in the circumferential direction may be measured.

Next, a dissimilar metal is clad on the outer or inner surface of the metal tube to form a clad tube. In this case, if the cladding conditions are inappropriate, defects will be generated at the joint interface between the metal pipe and the dissimilar metal. Further, depending on the overlay condition or the thickness variation of the metal pipe, the overlay thickness varies depending on the location.

Next, as shown in FIG. 2A, the ultrasonic probe 20 is arranged at a predetermined distance from the outer surface of the cladding tube 10 thus obtained. In addition, a couplant for efficiently transmitting and receiving ultrasonic waves is interposed between the outer surface of the cladding tube 10 and the ultrasonic probe 20. Water is usually used as the couplant.

The cladding tube 10 illustrated in FIG.
Is an inner cladding tube in which a dissimilar metal 14 is clad on the inner surface of a metal tube 12 having a tube thickness variation in the longitudinal direction. FIG.
1A illustrates a state in which defects 16, 16,... Are generated at the interface between the metal tube 12 and the dissimilar metal.

Next, the ultrasonic probe 20 is moved in the longitudinal direction using moving means (not shown) while rotating the cladding tube 10 around the axis using rotating means (not shown), and Inspection of the presence or absence of a defective echo is performed. Also in this case, when the metal tube 12 has a coarse crystal grain structure, longitudinal ultrasonic waves having broadband characteristics, in particular,
It is preferable to use longitudinal ultrasonic waves having a wide band characteristic of a frequency of 3 to 4 MHz.

At this time, as shown in FIG.
Time interval D₂Gates with surface echoes are observed
A predetermined time (hereinafter referred to as “gate position”).
U. ) D ₁Is set after the lapse of
₁Is changed according to the previously measured thickness of the metal tube 12.
You. That is, (D₁+ D₂/ 2) at the measurement point
Of the distance twice the thickness of the metal tube 12
Reach of surface echo and bottom echo of metal tube 12 before prime
Equivalent to the time difference. ) So that the game
G position D₁Should be changed.

When the metal tube 12 is, for example, a centrifugally cast tube, it is known that the thickness of the metal tube 12 varies greatly in the circumferential direction. For this reason, when ultrasonic inspection using the surface echo synchronization method is performed on the cladding tube 10 in which a dissimilar metal is clad in such a centrifugally cast tube, the gate is separated from the bonding interface, and the defect 16 cannot be detected. There is. Further, when the delay gate method is used, even when the thickness of the metal tube 12 does not fluctuate, if the distance between the overlaid cladding tube 10 and the ultrasonic probe 20 fluctuates, the gate is bonded. There is a case where a defect comes off the interface and a defect cannot be detected.

[0033] In contrast, varying the gate position D ₁ in accordance with the tube thickness variations of the padding before the metal tube 12 can be always set at the joint interface near the gate. If the time when the surface echo was observed is used as the reference for the gate position,
Even if the distance between the cladding tube 10 and the ultrasonic probe 20 fluctuates, the gate is always set near the bonding interface, and it is possible to detect defects with high accuracy.

Further, in the case where the metal tube 12 has a coarse crystal grain structure, the use of longitudinal ultrasonic waves having a wide band characteristic, in particular, longitudinal ultrasonic waves having a wide band characteristic of a frequency of 3 to 4 MHz, provides a high resolution. A defect echo is obtained.
Therefore, defects such as poor fusion at the bonding interface can be detected satisfactorily.

Next, a method for inspecting a cladding tube according to a third embodiment of the present invention will be described. Inspection method according to the present embodiment, when measuring the overlay thickness of the cladding tube in which the outer surface or the inner surface of the metal tube is clad with dissimilar metal, ultrasonic waves are incident on the cladding tube, the surface It is characterized in that the thickness of the cladding tube is measured from the difference between the arrival time of the echo and the bottom surface echo, and that the cladding thickness is determined from the difference between the thickness of the metal tube measured before the cladding. It is.

First, in the same manner as described above, the thickness of the metal tube before the cladding is measured in advance in the circumferential direction and the longitudinal direction of the metal tube, and then the different metal is clad on the outer or inner surface of the metal tube. . In this case, the method of measuring the thickness of the metal tube is not particularly limited. Ultrasonic waves are incident perpendicularly on the metal tube, and the difference between the arrival times of the surface echo and the bottom surface echo of the metal tube is measured. The point that the method of obtaining the tube thickness is preferable is the same as the detection method according to the above-described second embodiment. Further, when the metal tube has a coarse crystal grain structure, longitudinal ultrasonic waves having a broadband characteristic,
It is similar to the inspection method according to the second embodiment in that it is preferable to use longitudinal ultrasonic waves having a 4 MHz broadband characteristic.

Next, ultrasonic waves are vertically incident on the obtained cladding tube, and the difference in arrival time between the surface echo and the bottom surface echo of the cladding tube is measured. From the difference, the tube of the cladding tube is measured. Find the thickness. Also, at this time, the ultrasonic probe is moved in the longitudinal direction of the cladding tube while rotating the cladding tube around the axis, and the thickness of the cladding tube is determined in the circumferential direction and the longitudinal direction. . Also in this case, when the metal tube has a coarse crystal grain structure, longitudinal ultrasonic waves having a broadband characteristic,
It is preferable to use longitudinal ultrasonic waves having a wide band characteristic of ４4 MHz. Next, if the difference between the thickness of the cladding tube and the previously measured thickness of the metal tube is determined, the cladding thickness of the cladding tube can be determined.

When the difference between the acoustic impedance of the metal tube and the acoustic impedance of the dissimilar metal is small, even if ultrasonic waves are incident on the cladding tube, a reflected echo from the joint interface having a good joint state cannot be obtained. Therefore, it is difficult to directly measure the overlay thickness using the ultrasonic flaw detection method. On the other hand, by measuring the thickness of the metal tube before cladding and the thickness of the cladding tube, and determining the difference, even if the difference in acoustic impedance between the metal tube and the dissimilar metal is small, The embossed thickness can be measured accurately.

[0039]

EXAMPLE A cladding tube in which dissimilar metals were clad on the inner surface of a centrifugally cast tube by a cladding welding method was manufactured, and the presence or absence of a defect at a joint interface was examined using the method according to the present invention. In addition,
In preparing the cladding tube, the welding current was intentionally reduced during welding, and a fusion defect occurred at the joint interface. In measuring the defects, a change in the thickness of the centrifugally cast pipe before the cladding was measured in advance, and the gate position was changed according to the change in the pipe thickness. Further, a broadband focus type ultrasonic probe having a frequency of 3.5 MHz was used as the ultrasonic probe. The results are shown in FIG.

FIG. 3 shows that the distance from the end of the cladding tube (hereinafter referred to as "longitudinal position") is about 150 mm.
Up to this point, the height of the reflected echo from the joint interface of the cladding tube (hereinafter referred to as the "facing height of the cladding interface") is small, indicating that a good cladding tube is obtained. On the other hand, when the longitudinal position exceeds 150 mm, the build-up interface echo height increases. This area is
This corresponds to the region where the welding current of the overlay welding is lowered, and indicates that the fusion defect generated at the joint interface was detected by the method according to the present invention.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. It is. For example, in the above embodiment,
Although an example in which the present invention is applied to an inner cladding tube has been mainly described, the present invention can be similarly applied to an outer cladding tube. In this case, ultrasonic waves may be incident from the outer surface side of the outer cladding tube, or ultrasonic waves may be incident from the inner surface side of the outer cladding tube.

Further, in the above-described embodiment, the method of measuring the presence or absence of a defect or the tube thickness using one ultrasonic probe has been described. However, the method using two or more ultrasonic probes has been described. The presence or absence of a defect or the tube thickness may be measured simultaneously.

[0043]

According to the present invention, there is provided a method for detecting the magnitude of a reflected echo by irradiating an ultrasonic wave to a cladding tube in which a dissimilar metal is clad on the outer surface or inner surface of a metal tube having a coarse crystal grain structure. The use of longitudinal ultrasonic waves having a wide band characteristic of a frequency of 3 to 4 MHz as the ultrasonic waves has an effect that a high resolution can be obtained, and the presence or absence of a defect or the thickness of the overlay can be inspected with high accuracy.

When detecting a defect echo caused by a defect generated at the joint interface of the cladding tube, a gate for detecting the defect echo based on the thickness of the metal tube measured before the cladding. By changing the position, even when the thickness of the metal tube is not constant, or when the distance between the cladding tube and the ultrasonic probe fluctuates, the defect echo can be reliably detected. This has the effect.

Further, when measuring the thickness of the cladding tube, the thickness of the metal tube is measured before the cladding, and ultrasonic waves are incident on the cladding tube after the cladding, and the surface echo is measured. If the thickness of the cladding tube is measured from the difference between the arrival times of the bottom surface echo and the bottom echo, the cladding thickness can be easily and accurately obtained from the difference.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a frequency characteristic of an ultrasonic wave and a reflected echo.

FIG. 2 is a diagram illustrating a defect inspection method according to the present invention.

FIG. 3 is a diagram showing an example of detecting a defect generated on a joint surface of a cladding tube.

[Explanation of symbols]

 10 Overlay tube 12 Metal tube 14 Dissimilar metal 16 Defect

Continued on the front page F term (reference) 2F068 AA28 AA48 BB09 BB15 BB23 CC00 CC16 DD04 FF12 FF14 FF25 JJ12 JJ23 KK12 QQ02 2G047 AA07 AB01 BA03 BC07 BC18 CB01 GF11 GG02 GG30

Claims (5)

[Claims] 1. An inspection of a cladding tube provided with a reflection echo detecting step of irradiating an ultrasonic wave to a cladding tube in which dissimilar metal is clad on an outer surface or an inner surface of a metal tube and detecting a magnitude of a reflection echo. In the method, the metal tube has a coarse crystal grain structure, and a longitudinal wave ultrasonic wave having a wide band characteristic is used as the ultrasonic wave. 2. The ultrasonic wave has a frequency of 3 to 4 MHz.
The inspection method for a cladding tube according to claim 1, wherein z is z. 3. The metal tube has a crystal grain size of 100 to 10.
The overlay inspection method according to claim 1, wherein the thickness is 00 µm. 4. An inspection of a cladding tube provided with a reflection echo detecting step of irradiating an ultrasonic wave to a cladding tube in which dissimilar metal is clad on an outer surface or an inner surface of a metal tube and detecting a magnitude of a reflection echo. In the method, the reflection echo detecting step is to detect a defect echo caused by a defect generated at an interface between the metal tube and the dissimilar metal, and according to a tube thickness of the metal tube measured before the cladding. And a gate position adjusting step of changing a gate position for detecting the defect echo. 5. An inspection of a cladding tube provided with a reflection echo detecting step of irradiating an ultrasonic wave to a cladding tube in which a dissimilar metal is clad on an outer surface or an inner surface of a metal tube and detecting a magnitude of a reflection echo. In the method, the reflected echo detection step is to detect a surface echo caused by surface reflection of the cladding tube and a bottom echo caused by bottom reflection, and the thickness of the metal tube measured before cladding. And a cladding thickness calculating step of calculating a cladding thickness of the cladding tube from a difference between a thickness of the cladding tube and a thickness of the cladding tube determined from a difference between arrival times of the surface echo and the bottom surface echo. Inspection method of cladding tube characterized by having.